Hi,
Yes, Agnes was the daughter of James Hill, paper maker, of Polton Mill in Lasswade.
Alexander and Agnes are both recorded as living in High Street Parish at the time of their marriage.
Their first 2 children were then born in Alyth, Perthshire, and then the family moved North to Arbroath, Angus where the rest of their children were born.
I have also seen that there is some uncertainty in the son Alexander's age, but I am quite sure this is the correct census record as all the data ties in with Alexander's (senior) will and testament. There seems also to have only been one Galloway who was noted as a tailor in Edinburgh at that time.
In terms of religion I am not sure, but as I haven't seen anything to suggest they were catholic, then protestant is my best guess.